Lymphadenitis is the inflammation or enlargement of a lymph node. Lymph nodes are small, ovoid nodules normally ranging in size from a few millimeters to 2 cm. They are distributed in clusters along the course of lymphatic vessels located throughout the body. The primary function of lymph nodes is to filter out microorganisms and abnormal cells that have collected in lymph fluid.
Lymph node enlargement is a common feature in a variety of diseases and may serve as a focal point for subsequent clinical investigation of diseases of the reticuloendothelial system or regional infection. The majority of cases represent a benign response to localized or systemic infection. Most children with lymphadenitis exhibit small, palpable cervical, axillary, and inguinal lymph nodes. Less common is enlargement of the suboccipital or postauricular nodes. Palpable supraclavicular, epitrochlear, and popliteal lymph nodes are uncommon, as are enlarged mediastinal and abdominal nodes.
Lymphadenitis may affect a single node or a group of nodes (regional adenopathy) and may be unilateral or bilateral. The onset and course of lymphadenitis may be acute, subacute, or chronic.